Systems for fuel delivery

ABSTRACT

Various systems are provided for delivering fuel to an engine. In one example, a system includes a controller and a fluid system configured to maintain a fluid at a pressure downstream of a check valve. The controller may be configured to determine if a leak is present in the fluid system based on a first pressure decay rate of the fluid system, and responsive to identifying that a leak is present in the fluid system, differentiate between an internal leak and an external leak based on a leak flow rate as fluid system pressure decreases.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. Non-Provisional patentapplication Ser. No. 14/811,928, entitled “SYSTEMS FOR FUEL DELIVERY”,and filed on Jul. 29, 2015. The entire contents of the above-listedapplication are hereby incorporated by reference for all purposes.

BACKGROUND Technical Field

Embodiments of the subject matter disclosed herein relate to fueldelivery systems.

Discussion of Art

Vehicles include power sources, such as engines, which may be configuredto combust one or more fuel types, such as diesel and/or natural gas. Insome vehicles, liquid fuel is provided to the engine by a common railliquid fuel system. One type of common rail liquid fuel system comprisesa low-pressure fuel pump in fluid communication with a high-pressurefuel pump, and a fuel rail in fluid communication with the high-pressurefuel pump and further in fluid communication with at least one enginecylinder. The high-pressure fuel pump pressurizes fuel for deliverythrough the fuel rail. Fuel travels through the fuel rail to at leastone fuel injector, and ultimately to at least one engine cylinder wherefuel is combusted to provide power to the vehicle. In engines configuredto combust gaseous fuel such as natural gas, the gaseous fuel travelsthrough a gaseous fuel rail to at least one gas admission valve, andultimately to at least one engine cylinder where the gaseous fuel iscombusted to provide power to the vehicle.

In order to reduce the likelihood of engine degradation, the common railliquid fuel system may be monitored for fuel leaks. Once a leak isdetected, the engine is typically shut down to prevent enginedegradation and/or excessive emissions. However, such restrictive actionmay not be necessary if the leak is internal, e.g., if the leak is aleak from the high-pressure segment of the fuel system to thelow-pressure segment of the fuel system. Further engine degradation mayoccur if gaseous fuel gets trapped in the gaseous fuel rail at engineshutdown, as the gas admission valves may allow gaseous fuel to expandto the engine and/or exhaust, which can cause combustion issues leadingto engine degradation during a subsequent engine restart. However,simply venting the gaseous fuel to atmosphere comprises emissions.

Brief Description

In one example, a system includes a controller and a fluid systemconfigured to maintain a fluid at a pressure downstream of a checkvalve. The controller is configured to determine if a leak is present inthe fluid system based on a first pressure decay rate of the fluidsystem, and responsive to identifying that a leak is present in thefluid system, differentiate between an internal leak and an externalleak based on a leak flow rate as fluid system pressure decreases.

In another example, a system includes a controller and a gaseous fuelsupply system to supply gaseous fuel from a gaseous fuel storage sourceto an engine having a plurality of cylinders. The controller isconfigured to detect a request to shut down the engine, and in responseto detecting the request, remove gaseous fuel trapped within the gaseousfuel supply system by closing a gaseous fuel supply valve andselectively fueling gaseous fuel to the engine.

In a further example, a system includes an engine having a plurality ofcylinders configured to combust liquid fuel and gaseous fuel, a gaseousfuel supply system including a gaseous fuel rail having a plurality ofgas admission valves, each gas admission valve to supply gaseous fuel toa respective cylinder of the plurality of cylinders, and a gaseous fuelsupply valve located upstream of the gaseous fuel rail, an expansionchamber fluidically coupled to the gaseous fuel supply system, and acontroller. The controller is configured to detect a request to shutdown the engine, and in response to detecting the request, removegaseous fuel trapped within the gaseous fuel supply system by closingthe gaseous fuel supply valve and expanding the gaseous fuel in theexpansion chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an embodiment of a vehicle with anengine.

FIG. 2 shows a schematic diagram of an example cylinder of a multi-fuelengine.

FIG. 3 shows a schematic diagram of an example multi-fuel engine.

FIG. 4 is a flow chart illustrating an example method for a fueldelivery system.

FIGS. 5-6 are flow charts illustrating example methods for identifying aleak in a liquid fuel system.

FIG. 7 is a diagram illustrating an example relationship between a leakflow rate and system pressure for an internal and external leak.

FIG. 8 is a flow chart illustrating an example method for removinggaseous fuel trapped in a gaseous fuel rail.

DETAILED DESCRIPTION

Embodiments of the subject matter disclosed herein relate to fueldelivery systems for an engine of a vehicle, such as the vehicleillustrated in FIG. 1 and the engine illustrated in FIG. 2. The fueldelivery systems may include one or more of a liquid fuel system tosupply liquid fuel (e.g., diesel) to the engine and a gaseous fuelsystem to supply gaseous fuel (e.g., natural gas) to the engine, asshown in FIG. 3. The liquid fuel system and/or gaseous fuel system maybe controlled via a controller according to the methods illustrated inFIGS. 4-6 and 8. For example, the liquid fuel system may be monitoredfor leaks, as illustrated in FIG. 5, and if a leak is identified, theleak may be determined to be an internal or external leak, as shown inFIG. 6. The determination of whether the leak is internal or externalmay be based on the directionality of the leak flow rate as systempressure decreases, as shown by the graph of FIG. 7. In another example,the gaseous fuel system may be controlled to remove extra gaseous fuelin a gaseous fuel rail prior to, during, and/or after an engine shutdownand before a subsequent engine start, as shown in FIG. 8. By monitoringfor liquid fuel system leaks and/or removing trapped gaseous fuel,engine degradation and undesired emissions may be avoided.

The approach described herein may be employed in a variety of enginetypes, and a variety of engine-driven systems. Some of these systems maybe stationary, while others may be on semi-mobile or mobile platforms.Semi-mobile platforms may be relocated between operational periods, suchas mounted on flatbed trailers. Mobile platforms include self-propelledvehicles. Such vehicles can include on-road transportation vehicles, aswell as mining equipment, marine vessels, rail vehicles, and otheroff-highway vehicles (OHV). For clarity of illustration, a locomotive isprovided as an example of a self-propelled rail vehicle, and morebroadly, as an example of a mobile platform, supporting a systemincorporating an embodiment of the invention.

Before further discussion of the approach for delivering liquid and/orgaseous fuel while maintaining emission compliance and avoiding enginedegradation, an example of a platform is disclosed in which an enginemay be configured for a vehicle, such as a rail vehicle. For example,FIG. 1 shows a block diagram of an embodiment of a vehicle system 100,herein depicted as a rail vehicle or other vehicle 106 (e.g.,locomotive), configured to run on a rail 102 via a plurality of wheels112. As depicted, the rail vehicle includes an engine 104. In othernon-limiting embodiments, the engine may be a stationary engine, such asin a power-plant application, or an engine in a marine vessel or otheroff-highway vehicle propulsion system as noted above.

The engine receives intake air for combustion from an intake passage114. The intake passage receives ambient air from an air filter 160 thatfilters air from outside of the vehicle. Exhaust gas resulting fromcombustion in the engine is supplied to an exhaust passage 116. Exhaustgas flows through the exhaust passage, and out of an exhaust stack ofthe vehicle. In one example, the engine is a diesel engine that combustsair and diesel fuel through compression ignition. In other non-limitingembodiments, the engine may alternatively or additionally combust fuelincluding gasoline, kerosene, natural gas, biodiesel, or other petroleumdistillates of similar density through compression ignition (and/orspark ignition).

As depicted in FIG. 1, the engine is coupled to an electric powergeneration system, which includes an alternator/generator 122 andelectric traction motors 124. For example, the engine is a diesel and/ornatural gas engine that generates a torque output that is transmitted tothe generator which is mechanically coupled to the engine. In oneembodiment herein, engine is a multi-fuel engine operating with dieselfuel and natural gas, but in other examples engine may use variouscombinations of fuels other than diesel and natural gas.

The generator produces electrical power that may be stored and appliedfor subsequent propagation to a variety of downstream electricalcomponents. As an example, the generator may be electrically coupled toa plurality of traction motors and the generator may provide electricalpower to the plurality of traction motors. As depicted, the plurality oftraction motors are each connected to one of the plurality of wheels toprovide tractive power to propel the vehicle. One example configurationincludes one traction motor per wheel set. As depicted herein, six pairsof traction motors correspond to each of six pairs of motive wheels ofthe rail vehicle. In another example, alternator/generator may becoupled to one or more resistive grids 126. The resistive grids may beconfigured to dissipate excess engine torque via heat produced by thegrids from electricity generated by the alternator/generator.

In some embodiments, the vehicle system may include a turbocharger 120that is arranged between the intake passage and the exhaust passage. Theturbocharger increases air charge of ambient air drawn into the intakepassage in order to provide greater charge density during combustion toincrease power output and/or engine-operating efficiency. Theturbocharger may include a compressor (not shown) which is at leastpartially driven by a turbine (not shown). While in this case a singleturbocharger is included, the system may include multiple turbine and/orcompressor stages. Further, in some examples, the vehicle system mayadditionally or alternatively include a supercharger, where a compressoris driven by a motor, for example.

In some embodiments, the vehicle system may further include anaftertreatment system coupled in the exhaust passage upstream and/ordownstream of the turbocharger. In one embodiment, the aftertreatmentsystem may include a diesel oxidation catalyst (DOC) and a dieselparticulate filter (DPF). In other embodiments, the aftertreatmentsystem may additionally or alternatively include one or more emissioncontrol devices. Such emission control devices may include a selectivecatalytic reduction (SCR) catalyst, three-way catalyst, NOx trap, orvarious other devices or systems. In some examples, an aftertreatmentsystem may not be included in the vehicle system, and engine emissionsmay be controlled in an alternative manner, such as via exhaust gasrecirculation, described below.

The vehicle system may further include an exhaust gas recirculation(EGR) system 130 coupled to the engine, which routes exhaust gas fromthe exhaust passage of the engine to the intake passage downstream ofthe turbocharger. In some embodiments, the exhaust gas recirculationsystem may be coupled exclusively to a group of one or more donorcylinders of the engine (also referred to a donor cylinder system). Asdepicted in FIG. 1, the EGR system includes an EGR passage 132 and anEGR cooler 134 to reduce the temperature of the exhaust gas before itenters the intake passage. By introducing exhaust gas to the engine, theamount of available oxygen for combustion is decreased, thereby reducingthe combustion flame temperatures and reducing the formation of nitrogenoxides (e.g., NOx).

In some embodiments, the EGR system may further include an EGR valve forcontrolling an amount of exhaust gas that is recirculated from theexhaust passage of the engine to the intake passage of the engine. TheEGR valve may be an on/off valve controlled by a controller, or it maycontrol a variable amount of EGR, for example. As shown in thenon-limiting example embodiment of FIG. 1, the EGR system is ahigh-pressure EGR system. In other embodiments, the vehicle system mayadditionally or alternatively include a low-pressure EGR system, routingEGR from downstream of the turbine to upstream of the compressor.

As depicted in FIG. 1, the vehicle system further includes a coolingsystem 150. The cooling system circulates coolant through the engine toabsorb waste engine heat and distribute the heated coolant to a heatexchanger, such as a radiator 152. A fan 154 may be coupled to theradiator in order to maintain an airflow through the radiator when thevehicle is moving slowly or stopped while the engine is running. In someexamples, fan speed may be controlled by a controller. Coolant which iscooled by the radiator enters a tank 156. The coolant may then be pumpedby a water, or coolant, pump (not shown) back to the engine or toanother component of the vehicle system, such as the EGR cooler.

The vehicle further includes an engine controller 110 (referred tohereafter as the controller) to control various components related tothe vehicle. As an example, various components of the vehicle system maybe coupled to the controller via a communication channel or data bus. Inone example, the controller includes a computer control system. Thecontroller may additionally or alternatively include a memory holdingnon-transitory computer readable storage media (not shown) includingcode for enabling on-board monitoring and control of vehicle operation.

The controller may receive information from a plurality of sensors andmay send control signals to a plurality of actuators. The controller,while overseeing control and management of the vehicle, may beconfigured to receive signals from a variety of engine sensors, asfurther elaborated herein, in order to determine operating parametersand operating conditions, and correspondingly adjust various engineactuators to control operation of the vehicle. For example, the enginecontroller may receive signals from various engine sensors including,but not limited to, engine speed, engine load, intake manifold airpressure, boost pressure, exhaust pressure, ambient pressure, ambienttemperature, exhaust temperature, engine coolant pressure, gastemperature in the EGR cooler, or the like. Correspondingly, thecontroller may control the vehicle by sending commands to variouscomponents such as the traction motors, the alternator/generator,cylinder valves, fuel injectors, a notch throttle, or the like. Otheractuators may be coupled to various locations in the rail vehicle.

FIG. 2 depicts an embodiment of a combustion chamber, or cylinder 200,of a multi-cylinder internal combustion engine, such as the enginedescribed above with reference to FIG. 1. The cylinder may be defined bya cylinder head 201, housing the intake and exhaust valves and liquidfuel injector, described below, and a cylinder block 203.

The engine may be controlled at least partially by a control systemincluding controller 110 which may be in further communication with avehicle system, such as the locomotive described above with reference toFIG. 1. As described above, the controller may further receive signalsfrom various engine sensors including, but not limited to, engine speed,engine load, boost pressure, exhaust pressure, ambient pressure, CO₂levels, exhaust temperature, NO_(x) emission, engine coolant temperature(ECT) from temperature sensor 230 coupled to cooling sleeve 228, etc.Correspondingly, the controller may control the vehicle system bysending commands to various components such as alternator, cylindervalves, throttle, fuel injectors, etc.

The cylinder (i.e., combustion chamber) may include cylinder liner 204with a piston 206 positioned therein. The piston may be coupled to acrankshaft 208 so that reciprocating motion of the piston is translatedinto rotational motion of the crankshaft. In some embodiments, theengine may be a four-stroke engine in which each of the cylinders firesin a firing order during two revolutions of the crankshaft. In otherembodiments, the engine may be a two-stroke engine in which each of thecylinders fires in a firing order during one revolution of thecrankshaft.

The cylinder receives intake air for combustion from an intake includingan intake passage 210. The intake passage receives intake air via anintake manifold. The intake passage may communicate with other cylindersof the engine in addition to the cylinder, for example, or the intakepassage may communicate exclusively with the cylinder.

Exhaust gas resulting from combustion in the engine is supplied to anexhaust including an exhaust passage 212. Exhaust gas flows through theexhaust passage, to a turbocharger in some embodiments (not shown inFIG. 2) and to atmosphere, via an exhaust manifold. The exhaust passagemay further receive exhaust gases from other cylinders of the engine inaddition to the cylinder, for example.

Each cylinder of the engine may include one or more intake valves andone or more exhaust valves. For example, the cylinder is shown includingat least one intake poppet valve 214 and at least one exhaust poppetvalve 216 located in an upper region of cylinder. In some embodiments,each cylinder of the engine, including the cylinder, may include atleast two intake poppet valves and at least two exhaust poppet valveslocated at the cylinder head.

The intake valve may be controlled by the controller via an actuator218. Similarly, the exhaust valve may be controlled by the controllervia an actuator 220. During some conditions, the controller may vary thesignals provided to the actuators to control the opening and closing ofthe respective intake and exhaust valves. The position of the intakevalve and the exhaust valve may be determined by respective valveposition sensors 222 and 224, respectively, and/or by cam positionsensors. The valve actuators may be of the electric valve actuation typeor cam actuation type, or a combination thereof, for example.

The intake and exhaust valve timing may be controlled concurrently orany of a possibility of variable intake cam timing, variable exhaust camtiming, dual independent variable cam timing or fixed cam timing may beused. In other embodiments, the intake and exhaust valves may becontrolled by a common valve actuator or actuation system, or a variablevalve timing actuator or actuation system. Further, the intake andexhaust valves may by controlled to have variable lift by the controllerbased on operating conditions.

In still further embodiments, a mechanical cam lobe may be used to openand close the intake and exhaust valves. Additionally, while afour-stroke engine is described above, in some embodiments a two-strokeengine may be used, where the intake valves are dispensed with and portsin the cylinder wall are present to allow intake air to enter thecylinder as the piston moves to open the ports. This can also extend tothe exhaust, although in some examples exhaust valves may be used.

In some embodiments, each cylinder of the engine may be configured withone or more fuel injectors for providing fuel thereto. As a non-limitingexample, FIG. 2 shows the cylinder including a fuel injector 226. Thefuel injector is shown coupled directly to the cylinder for injectingfuel directly therein. In this manner, the fuel injector provides whatis known as direct injection of a fuel into the combustion cylinder. Thefuel may be delivered to the fuel injector from a first, liquid fuelsystem 232, including a fuel tank, fuel pumps, and a fuel rail(described in more detail with respect to FIG. 3). In one example, thefuel is diesel fuel that is combusted in the engine through compressionignition. In other non-limiting embodiments, the fuel may be gasoline,kerosene, biodiesel, or other petroleum distillates of similar densitythrough compression ignition (and/or spark ignition).

Further, each cylinder of the engine may be configured to receivegaseous fuel (e.g., natural gas) alternative to or in addition to dieselfuel. The gaseous fuel may be provided to the cylinder via the intakemanifold, as explained below. As shown in FIG. 2, the intake passage mayreceive a supply of gaseous fuel from a second, gaseous fuel system 234,via one or more gaseous fuel lines, pumps, pressure regulators, etc.,located upstream of the cylinder. In some embodiments, the gaseous fuelsystem may be located remotely from the engine, such as on a differentvehicle (e.g., on a fuel tender car), and the gaseous fuel may besupplied to the engine via one or more fuel lines that traverse theseparate vehicles. However, in other embodiments the gaseous fuel systemmay be located on the same vehicle as the engine.

A plurality of gas admission valves, such as gas admission valve 236,may be configured to supply gaseous fuel from the gaseous fuel system toeach respective cylinder via respective intake passages. For example, adegree and/or duration of opening of the gas admission valve may beadjusted to regulate an amount of gaseous fuel provided to the cylinder.As such, each respective cylinder may be provided with gaseous fuel froman individual gas admission valve, allowing for individual cylindercontrol in the amount of gaseous fuel provided to the cylinders.However, in some embodiments, a single-point fumigation system may beused, where gaseous fuel is mixed with intake air at a single pointupstream of the cylinders. In such a configuration, each cylinder may beprovided with substantially similar amounts of gaseous fuel. To regulatethe amount of gaseous fuel provided by the single-point fumigationsystem, in some examples a gaseous fuel control valve may be positionedat a junction between a gaseous fuel supply line and the engine intakeair supply line or intake manifold. The gaseous fuel control valvedegree and/or duration of opening may be adjusted to regulate the amountof gaseous fuel admitted to the cylinders. In other examples, the amountof gaseous fuel admitted to the cylinders in the single-point fumigationsystem may be regulated by another mechanism, such as control of agaseous fuel regulator, via control of a gaseous fuel pump, etc.

FIG. 3 illustrates multiple cylinders of engine 104, including cylinder200, cylinder 302, cylinder 304, and cylinder 306. While four cylindersarranged in-line are illustrated in FIG. 3, such an arrangement isnon-limiting, and other engine configurations are possible. For example,the engine may be a V-6, V-8, V-12, V-16, I-6, I-8, or other enginetype. The engine may be supplied one or more of liquid fuel from theliquid fuel system and gaseous fuel from the gaseous fuel system. Assuch, each cylinder of the engine includes a liquid fuel injector,including injector 226 as well as injectors 308, 310, and 312. Eachliquid fuel injector is supplied with liquid fuel from a common fuelrail 314. The common fuel rail may be supplied with fuel from a liquidfuel tank 316 (e.g., a diesel fuel storage tank).

A low-pressure fuel pump 340 is in fluid communication with the fueltank. In this embodiment, the low-pressure fuel pump is disposed insideof the fuel tank and can be immersed below the liquid fuel level. Inalternative embodiments, the low-pressure fuel pump may be coupled tothe outside of the fuel tank and pump fuel through a suction device.Operation of the low-pressure fuel pump is regulated by the controller.

Liquid fuel is pumped by the low-pressure fuel pump from the fuel tankto a high-pressure fuel pump 342 through a conduit 344. A valve 346 isdisposed in the conduit and regulates fuel flow through the conduit. Forexample, the valve is an inlet metering valve (IMV). The IMV is disposedupstream of the high-pressure fuel pump to adjust a flow rate of fuelthat is provided to the high-pressure fuel pump and further to thecommon fuel rail for distribution to the plurality of liquid fuelinjectors for fuel injection. For example, the IMV may be a solenoidvalve, opening and closing of which is regulated by the controller. Inother words, the controller commands the IMV to be fully closed, fullyopen, or a position in between fully closed and fully opened in order tocontrol fuel flow to the high-pressure fuel pump to a commanded fuelflow rate. During operation of the vehicle, the IMV is adjusted to meterfuel based on operating conditions, and during at least some conditionsmay be at least partially open. It is to be understood that the valve ismerely one example of a control device for metering fuel and anysuitable control element may be employed without departing from thescope of this disclosure. For example, a position or state of the IMVmay be electrically controlled by controlling an IMV electrical current.As another example, a position or state of the IMV may be mechanicallycontrolled by controlling a servo motor that adjusts the IMV.

The high-pressure fuel pump increases fuel pressure from a lowerpressure to a higher pressure. The high-pressure fuel pump is fluidlycoupled with the common fuel rail. The high-pressure fuel pump deliversfuel to the common fuel rail through a conduit 348. The high-pressurepump includes a check valve 350 configured to allow forward flow of fuelfrom the high-pressure pump to the conduit 348 while preventing backflowfrom and/or through the high-pressure pump. The plurality of fuelinjectors are in fluid communication with the common fuel rail. Each ofthe plurality of fuel injectors delivers fuel to one of a plurality ofengine cylinders in the engine. Fuel is combusted in the plurality ofengine cylinders to provide power to the vehicle through an alternatorand traction motors, for example. Operation of the plurality of fuelinjectors is regulated by the controller. In the embodiment of FIG. 3,the engine includes four fuel injectors and four engine cylinders. Inalternative embodiments, more or fewer fuel injectors and enginecylinders can be included in the engine.

Fuel pumped from the fuel tank to an inlet of the IMV by thelow-pressure fuel pump may operate at what is referred to as a lowerfuel pressure or engine fuel pressure. Correspondingly, components ofthe liquid fuel system which are upstream of the high-pressure fuel pumpoperate in a lower fuel pressure or engine fuel pressure region. On theother hand, the high-pressure fuel pump may pump fuel from the lowerfuel pressure to a higher fuel pressure or rail fuel pressure.Correspondingly, components of the liquid fuel system which aredownstream of the high-pressure fuel pump are in a higher-fuel pressureor rail fuel pressure region.

A fuel pressure in the lower fuel pressure region is measured by a firstpressure sensor 352 that is positioned in the conduit 344. The firstpressure sensor sends a pressure signal to the controller. In analternative application, the first pressure sensor is in fluidcommunication with an outlet of the low-pressure fuel pump. A fueltemperature in the lower fuel pressure region is measured by atemperature sensor 354 that is positioned in conduit 344. Thetemperature sensor sends a temperature signal to the controller.

A fuel pressure in the higher fuel pressure region is measured by asecond pressure sensor 356 that is positioned in the conduit 348. Thesecond pressure sensor sends a pressure signal to the controller. In analternative application, the second pressure sensor is in fluidcommunication with an outlet of the high-pressure fuel pump. Note thatin some applications various operating parameters may be generallydetermined or derived indirectly in addition to or as opposed to beingmeasured directly.

Each cylinder of engine may similarly include a gas admission valve tosupply gaseous fuel, including gas admission valve 236 as well as gasadmission valves 322, 324, and 326. Each gas admission valve may bepositioned in an intake passage of a respective cylinder, or othersuitable location. The gas admission valves may be supplied gaseousfuel, such as natural gas, from a gaseous fuel rail 328. The gaseousfuel rail may receive gaseous fuel from a gaseous fuel tank (such as anLNG storage tank 330) via a gaseous fuel supply line 332. Control offlow of gaseous fuel to the gaseous fuel rail may be controlled viagaseous fuel supply valve 334. Further, the pressure of the gaseous fuelmay be controlled by one or more regulators (not shown). In someexamples, the LNG storage tank may be located remotely from engine, suchas on board a fuel tender, and may supply fuel to the gaseous fuelsupply line via a fluidic coupling. In other examples, the gaseous fuelstorage tank may located on board the same vehicle as the engine.Further, in some embodiments, the individual gas admission valves may bedispensed with, and all the cylinders may be supplied with the samegaseous fuel/intake air mixture from an upstream single-point fumigationsystem.

Each liquid fuel injector of each cylinder, as well as each gasadmission valve of each cylinder, may be individually controlled by acontroller (such as controller 110) to enable individual cylindercontrol of the fuel supply. Accordingly, each cylinder may be operatedwith varying levels of liquid fuel and/or gaseous fuel. In someembodiments, the liquid fuel injectors may be controlled by a differentcontroller than the controller that controls the gas admission valves.Further, in a gaseous fumigation system, rather than controlling theindividual gas admission valves, a single gaseous fuel control valve orother gaseous fuel control element may be controlled by the controllerto regulate the amount of gaseous fuel admitted to the cylinders.

In an example, a mixture of gaseous fuel and air may be provided tocylinder 200 via the intake passage and, in some embodiments, the gasadmission valve. Then, during compression, diesel fuel may be injectedto cylinder 200 via fuel injector 226. The diesel fuel may be ignitedvia compression ignition and subsequently ignite the gaseous fuel.Similar combustion events may occur for each cylinder of engine.

In addition to the sensors mentioned above, the controller receivesvarious signals from a plurality of engine sensors coupled to the enginethat may be used for assessment of fuel control health and associatedengine operation. For example, the controller receives sensor signalsindicative of air-fuel ratio, engine speed, engine load, enginetemperature, ambient temperature, fuel value, a number of cylindersactively combusting fuel, etc. In the illustrated implementation, thecontroller is a computing device, such as microcomputer that includes aprocessor unit 358, non-transitory computer-readable storage mediumdevice 359, input/output ports, memory, and a data bus.Computer-readable storage medium included in the controller isprogrammable with computer readable data representing instructionsexecutable by the processor for performing the control routines andmethods described below as well as other variants that are notspecifically listed.

The controller is operable to adjust various actuators based ondifferent operating parameters received or derived from differentsignals received from the various sensors, to dynamically assess thehealth of the liquid fuel system, for example, and control operation ofthe engine based on the assessment. For example, the controller isoperable to check the integrity of the liquid fuel system for fuelleaks, for example after maintenance periods. Such an assessment checksfor small leaks that are most likely to occur after improper maintenanceso that they can be addressed before becoming bigger fuel leaks. Inparticular, the controller is operable during a no-load condition of theengine, to stop fuel injection by the plurality of fuel injectors andclose the IMV. A no-load condition of the engine occurs when the engineis rotated by inertia or an external torque generated from outside ofthe engine. As one example, a no-load condition occurs during enginestartup when a cranking motor turns the engine. The turning enginedrives the fuel pumps to pressurize the common fuel rail. As anotherexample, a no-load condition occurs when a motor/generator powers theengine. As yet another example, a no-load condition occurs when theengine absorbs torque or creates negative or brake torque, such asduring a coast down event. A coast down event occurs when an engine isoperating at speed and the demanded engine load becomes zero (orno-load) and the engine is rotated by inertia until external resistanceslows the engine speed to a designated speed or the demanded engine loadincreases. Stated another way, a no-load condition of the engine is acondition where fuel injection is not necessary to meet an engine load.The post-maintenance assessment is performed during no-load conditionsof the engine so that fuel injection can be stopped without interferingwith engine operation.

Once fuel injection is stopped and the IMV is closed, the controllermonitors fuel pressure decay in the common fuel rail for a firstdesignated duration. The first duration may be designated or selectedbased on operating conditions, and may be a predetermined duration. Ifthe fuel rail pressure decay rate of the fuel pressure in the commonfuel rail is greater than a decay rate threshold after the firstdesignated duration, the controller is operable to set a degradationcondition. If the fuel rail pressure decay rate is less than the decayrate threshold, fuel injection is restarted and engine operationcontinues. Fuel pressure decay refers to a drop or reduction in fuelpressure over time. Fuel pressure decay is monitored during theaforementioned control conditions (injection stopped and the IMV closed)because under such conditions, fuel should be neither significantlyleaving nor entering the common fuel rail. Thus, a fuel pressure decayrate greater than the decay rate threshold is indicative of a possibleleak condition.

In some implementations, the controller is operable to check thatoperating conditions are suitable prior to monitoring fuel pressuredecay for determining possible fuel leaks. For example, the controlleris operable to check that the low-pressure fuel pump is pumping fuel tothe common fuel rail so that there is enough fuel pressure built up todetermine or measure fuel pressure decay. Correspondingly, thecontroller is operable to check that the engine is operating in adesignated engine speed range where the engine is cranking to operatethe fuel pump. By checking that such conditions are in effect, thelikelihood of a false positive assessment of a fuel leak in the liquidfuel system may be reduced. Furthermore, the controller is operable toset a degradation condition if the fuel rail pressure is less than arail fuel pressure threshold for a second designated duration when suchconditions are in effect (e.g., the engine fuel pressure at an inlet ofthe IMV is greater than an engine fuel pressure threshold and an enginespeed is in a designated engine speed range). The second designatedduration may be the same or different from the first designated durationfor monitoring fuel pressure decay. In one example, the first designatedduration is 0.2 seconds and the second designated duration is 30seconds. In other words, if the engine is cranking and the low-pressurefuel pump is pumping fuel, but the fuel pressure is not building beyondthe fuel pressure threshold after the second designated duration, thenit is assumed that a fuel leak exists or a component of the liquid fuelsystem is degraded.

In some implementations, the degradation condition may include setting adiagnostic flag and presenting an indication (e.g., visual or audio) ofthe degradation condition to an operator. In some implementations, thedegradation condition may include shutting down the engine. By shuttingdown the engine in response to detection of a fuel leak, the likelihoodof engine degradation, degraded drivability, or the like may be reduced.However, not all fuel leaks may cause engine degradation. For example,if the check valve in the high-pressure fuel pump were to becomedegraded such that it did not prevent backflow of fuel, the fuel wouldstill be contained within the liquid fuel system, and thus combustionstability and/or emissions issues would not occur. If the engine wereautomatically shut down in response to a degraded check valve, it mayunnecessarily strand the vehicle, delaying arrival of the vehicle at itsdestination and potentially increasing maintenance costs. Thus,according to embodiments disclosed herein, after it is determined that aleak is present in the liquid fuel system, the leak may bedifferentiated as being either internal or external based on thedirectionality of the leak flow rate as system pressure decreases. Ifthe leak is determined to be internal, the engine may continue tooperate, avoiding an unnecessary engine shut down. Additional detailsregarding detecting a liquid fuel system leak are presented below withrespect to FIGS. 4-7.

In some examples, the liquid fuel rail may include a pressure reliefvalve. The pressure relief valve may be a manual valve that can beopened to relive the pressure during high pressure system maintenance.However, if the valve is improperly closed, the system will not developfuel pressure. For example, conventional handle design may be symmetric.Due to the symmetric design of the handle, sometimes a field operatormay misjudge the valve to be in the open instead of closed position,which may lead to a leak the pressure in common rail fuel system.

To prevent such position errors, a pressure relief valve with anasymmetric handle 370 may be present. As shown in FIG. 3, the pressurerelief valve may appear differently when in the open position 372 thanwhen in the closed position 374. For example, the valve handle may havemultiple protrusions or markings that assume a different orientationwhen in the open vs. closed position.

Further, the handle may be marked with OPEN & CLOSED markings. Thehandle may be removable and may be slipped on to the valve shaft priorto opening or closing the valve. The handle and shaft may be designedsuch that the handle can only slip/engage on the shaft in one (thecorrect) position. In this way, the handle cannot be improperly placedon the shaft—this ensures that the valve OPEN/CLOSED position is alwaysright/correct. After closing/opening the valve, operator can be certainof the position of the valve, and if the valve is not closed it will bevisible clearly.

As explained previously, in some examples the engine is configured tocombust gaseous fuel, such as natural gas. The gaseous fuel is suppliedto the plurality of cylinders via respective gas admission valves, whichreceive the gaseous fuel via a gaseous fuel rail. To supply gaseous fuelto the engine, the gaseous fuel is maintained at a greater pressure thanintake air pressure. Upon shutdown, the engine intake air pressurebecomes near atmospheric. This results in a positive pressuredifferential between the gaseous fuel supply and engine intake. Thepressure differential value will vary depending upon engine power at theinstance of shutdown, with the maximum occurring at the engine's highestboost intake air pressure. Upon shutdown there will be a finite amountof gaseous fuel trapped between the gaseous fuel supply valve andindividual cylinder gas admission valves. Typically, gas admissionvalves do not provide sufficient sealing capability. This trapped gaspressure will be relieved by the inherent leakage rate of the gasadmission valves. The gaseous fuel may expand into the engine's intakeand exhaust systems. During this expansion the gaseous fuel will mixwith air and create zones that will be initially too rich forcombustion. As the gaseous fuel disperses, the gaseous fuel-air mixturewill pass through the combustibility range of the gaseous fuel in air(˜5-10%). If the engine is shut-down for an extended period of time, thegaseous fuel-air ratio may become too lean for combustion. Risk existsfor engine degradation and potential operator safety at engine restartunless the trapped gaseous fuel can be prevented from entering ashut-down engine.

Thus, to prevent engine degradation, the gaseous fuel may be removedfrom the gaseous fuel rail prior to engine shutdown and/or prior to asubsequent engine start. In one example, the gaseous fuel supply valvecontrolling flow of gaseous fuel into the gaseous fuel rail may beclosed and the gaseous fuel in the rail may be selectively supplied tothe cylinders for a duration prior to engine shutdown or prior to enginestart up. The gaseous fuel may be combusted (e.g., supplied to thecylinders along with liquid fuel) or it may be passed through the enginewithout combusting.

In another example, the gaseous fuel trapped in the rail may be expandedin an expansion chamber 360 fluidically coupled to the gaseous fuelrail. The expansion chamber may be a cylinder or other accumulator thatis configured to hold the gaseous fuel as it expands out of the rail.The additional volume provided by the expansion chamber may reduce thepressure of the gaseous fuel in the rail (e.g., to atmosphericpressure), such that it does not leak through the gas admission valves.The expansion chamber may include a diaphragm coupled to a spring and aline fluidically coupled to the intake manifold to urge the gaseous fuelback into the gaseous fuel rail during a subsequent engine start, wherethe gaseous fuel can be combusted. In other examples, the expansionchamber may include a pneumatic, hydraulic, or electric actuator to pushthe gaseous fuel back to the rail. The chamber may be of a sufficientsize to allow the maximum amount of trapped gaseous fuel to reachatmospheric pressure.

In a further example, in addition or alternative to having an expansionchamber, the gaseous fuel system may include a gaseous fuel canisterfluidically coupled to the gaseous fuel rail (e.g., the canister may beincluded in the gaseous fuel system in place of the expansion chamber)that may include charcoal or other absorbent material to traphydrocarbons in the gaseous fuel that is vented from the gaseous fuelrail at engine shutdown. The gaseous fuel canister may be coupled toatmosphere, such that as the gaseous fuel is vented from the gaseousfuel rail (e.g., by opening the vent valve in the vent line coupling thegaseous fuel canister to the gaseous fuel rail), the gaseous fueltravels through the absorbent material in the canister, where thehydrocarbons are trapped and any air or other gas is vented toatmosphere. At a subsequent start-up, or when the canister material isfully loaded with hydrocarbons, a purge may be performed where a vacuumsource is applied to the canister to strip the hydrocarbons off theabsorbent material and direct the hydrocarbons back to the gaseous fuelrail for combustion.

In a still further example, an ignition source 362 may be present in avent line 364 fluidically coupled to the gaseous fuel rail. When a ventvalve 366 is open, the gaseous fuel travels out of the rail and throughthe vent line, where it will be vented to atmosphere, or if the ignitionsource is activated, combusted prior to reaching atmosphere. Theignition source may be a spark plug or other suitable component capableof igniting the gaseous fuel. Additional details regarding removinggaseous fuel trapped in a gaseous fuel rail are presented below withrespect to FIGS. 4 and 8.

Turning now to FIG. 4, a method 400 for a fuel delivery system ispresented. Method 400 may be carried out according to instructionsstored on a memory of a controller, such as controller 110 describedabove. Method 400 may be carried out in conjunction with various sensorsand/or actuators of one or more fuel delivery systems, such as liquidfuel system 232 and gaseous fuel system 234 of FIGS. 2-3. At 402, method400 includes determining operating parameters. The determined operatingparameters may include, but are not limited to, engine speed, engineoutput, throttle position, engine status (e.g., engine shutdown or startup requested), combustion fuel status (e.g., if the engine is operatingwith one of or both a liquid and gaseous fuel), elapsed time since aprevious leak detection test was carried out, and other parameters.

At 404, method 400 delivers liquid and/or gaseous fuel to the engine. Insome examples, only liquid fuel may be delivered to the engine, and thus100% of the engine power is derived from liquid fuel. In other examples,only gaseous fuel may be delivered to the engine, and thus 100% of theengine power is derived from gaseous fuel. In still further examples,both liquid and gaseous fuel may be delivered to the engine, and thus aportion of the engine power may be derived from liquid fuel and aportion of the engine power may be derived from gaseous fuel. Therelative amounts of the different fuels delivered to the engine may bebased on the engine type (whether the engine is configured to operatewith only liquid fuel, only gaseous fuel, or both), engine speed and/oroutput, and/or additional parameters.

At 406, method 400 includes determining if a liquid fuel system leaktest is indicated. The leak test may be performed if a threshold amountof time has elapsed since a previous leak test was performed, or inresponse to other suitable parameters. If the leak test is indicated,method 400 proceeds to 408 to perform the leak detection test accordingto the method described below with respect to FIG. 5. If the leakdetection test is not to be performed, method 400 proceeds to 410 todetermine if a non-emergency engine shutdown request has been received,for example from a vehicle operator. If the leak test is performed,method 400 may still progress to 410 to determine if the non-emergencyengine shutdown has been requested, upon completion of the leak test.

A non-emergency shutdown may include a standard shutdown that isperformed upon request from a vehicle operator and/or upon completion ofa vehicle trip, for example, as opposed to an emergency shutdownrequest, which may be performed automatically by the controller or bythe vehicle operator in response to an emergency condition, such as adegraded engine component that could cause catastrophic engine orvehicle degradation if the vehicle were allowed to continue to operate.During an emergency shutdown, non-essential tasks that may be completedat shutdown, such as the removal of trapped gaseous fuel, describedbelow, may be dispensed with in order to expedite shutdown.

Accordingly, if a non-emergency shutdown request is not received, method400 proceeds to 412 to either perform an emergency shutdown if anemergency shutdown request is received, or to maintain current operatingparameters (e.g., continue to deliver liquid and/or gaseous fuel at thespecified amounts) if no engine shutdown request is received. Method 400then returns.

If a non-emergency shutdown request is received, method 400 proceeds to414 to determine if gaseous fuel is present in the gaseous fuel rail.For example, if the engine is currently operating with gaseous fuel, itmay be determined that at least some gaseous fuel is likely to bepresent in the gaseous fuel rail. However, if the engine is notcurrently combusting gaseous fuel, or has not combusted gaseous fuel fora threshold amount of time, it may be determined that no gaseous fuel islikely to be present in the gaseous fuel rail. Other mechanisms fordetermining if gaseous fuel is present in the gaseous fuel rail arepossible, such as based on output from a gaseous fuel rail pressuresensor.

If it is determined that no gaseous fuel is present in the gaseous fuelrail, method 400 proceeds to 416 to cease fuel injection (e.g., liquidfuel injection) according to a standard, non-emergency shutdown protocolin order to shutdown the engine. Method 400 then returns. If it isdetermined that at least some gaseous fuel is present in the gaseousfuel rail, method 400 proceeds to 418 to remove trapped gaseous fuelfrom the gaseous fuel rail prior to a subsequent engine start up,according to the method that will be described below with respect toFIG. 8. Method 400 then returns.

FIG. 5 is a flow chart illustrating a method 500 for determining if aleak is present in a common rail liquid fuel system, such as the liquidfuel system of FIGS. 2-3. In one example, the method 500 is executableby the controller 110, and may be performed as part of method 400, forexample in response to an indication that a leak detection test isindicated. At 502, the method 500 includes determining if there iscurrently a no-load condition of the engine. A no-load condition of theengine may occur when the engine is rotated by inertia or an externaltorque generated from outside of the engine. As one example, a no-loadcondition occurs during engine startup when a cranking motor turns theengine. The turning engine drives the fuel pumps to pressurize thecommon fuel rail. As another example, a no-load condition occurs when amotor/generator powers the engine. As yet another example, a no-loadcondition occurs when the engine absorbs torque or creates negative orbrake torque, such as during a coast down event. Stated another way, ano-load condition of the engine is a condition where fuel injection isnot necessary to meet an engine load. In other examples, a no-loadcondition may occur during idling, where the engine is operated to keepthe engine running and to power auxiliary loads, but no power isprovided for propulsion. If a no-load condition exists, the method 500moves to 504. Otherwise, the method 500 returns to 502.

At 504, the method 500 includes determining if a liquid fuel railpressure is greater than a rail pressure threshold. The determinationperformed at 504 checks to see if the liquid fuel rail pressure isalready built up to a sufficient level for operation. The rail pressurethreshold may be set to any suitable pressure level. In one example, therail pressure threshold is set to 40,000 kPa. If the fuel rail pressureis greater than the rail pressure threshold, the method 500 returns toother operations. Otherwise, the method 500 moves to 506.

At 506, the method 500 includes determining if the liquid fuel railpressure becomes greater than the rail pressure threshold for a seconddesignated duration while an engine fuel pressure is greater than anengine pressure threshold and an engine speed is in a designated enginespeed range. The engine fuel pressure represents the pressure of fuelprovided by the low-pressure fuel pump at the inlet of the IMV. Theengine speed range determination checks to see if the engine is actuallycranking to drive the low-pressure fuel pump. The engine fuel pressuredetermination checks to see if fuel is actually being provided to theIMV to build pressure in the common fuel rail. If the engine is crankingand the engine fuel pressure is less than the engine pressure threshold,then it can be assumed that there is an insufficient engine fuelpressure to operate the engine and the low-pressure fuel pump may or maynot be functioning properly. Accordingly, the method 500 moves to 518.If the engine is cranking and the engine fuel pressure is buildingpressure beyond the threshold the method 500 moves to 508.

At 508, the method 500 includes determining if the liquid fuel railpressure is greater than the rail pressure threshold. If the engine iscranking (e.g., engine speed in speed range) and the low-pressure fuelpump is pumping fuel (e.g., engine fuel pressure>engine pressurethreshold), but the fuel rail is not pressurizing (e.g., the fuel railpressure<rail pressure threshold), then it can be assumed that there isa leak in the high pressure fuel system or another type of degradationand the method 500 moves to 518. Otherwise, if the engine is cranking,the low-pressure fuel pump is operating, and the fuel rail pressure isbuilt up to a sufficient pressure level to test for fuel pressure decay,then the method 500 moves to 510.

The second designated duration, the engine fuel pressure threshold, andthe engine speed range may be set to any suitable values. In oneexample, the second designated duration is 30 seconds, the rail fuelpressure threshold is 40,000 kPa, the engine fuel pressure threshold isapproximately 241 kPa and the designated engine speed range is between35 and 325 RPM. If the fuel rail pressure remains greater than the railpressure threshold for during these operating conditions, the method 500moves to 510. Otherwise, it can be assumed that there is degradation ofthe liquid fuel system, such as a gross fuel leak, since fuel railpressure is unable to remain above the rail pressure threshold. If thefuel pressure becomes less than the rail fuel pressure threshold for theselected duration, the method moves to 518.

At 510, the method 500 includes stopping fuel injection by the pluralityof fuel injectors. In one example, stopping fuel injection includescontrolling a pulse width modulation signal to command the plurality offuel injectors to not inject fuel. In some implementations, stoppingfuel injection includes turning off a fuel pump that provides fuel to aninlet of the inlet metering valve. Moreover, the fuel injection may bestopped in any suitable way including preventing fuel from entering ahigh-pressure fuel pump that supplies fuel to the fuel rail, such as byclosing an additional cut-off valve or the like.

At 512, the method 500 includes closing the IMV. In one example, closingthe IMV includes commanding an IMV electrical current for controlling aposition of the IMV to be increased to an electrical current thatcorresponds to a fully closed position.

At 514, the method 500 includes verifying closure of the IMV prior toinitiating a predetermined duration for measuring a fuel pressure decayrate of the common fuel rail. In one example, verifying closure of theIMV includes starting the first designated duration in response to theIMV electrical current being greater than an electrical currentthreshold. The electrical current threshold is set to an electricalcurrent that corresponds to the fully closed position of the IMV. In oneexample, the electrical current threshold is set to 1.8 Amps. Byverifying closure of the IMV, a determination accuracy of the fuelpressure decay rate may be increased.

At 516, the method 500 includes determining if a fuel rail pressuredecay rate of a fuel pressure in the common fuel rail is greater than adecay threshold after a first designated duration. The pressure decayrate and the first designated duration may be set to any suitable value.In one example, the decay threshold is 500 kPa and the first designatedduration is 0.2 seconds. If the fuel rail pressure decay rate is greaterthan the decay threshold, the method 500 moves to 518. Otherwise, it isdetermined that a fuel leak does not exist and the method 500 returns toother operations.

At 518, the method 500 includes indicating that a fuel leak is presentand determining if the leak is internal or external according to themethod described below with respect to FIG. 6. If the leak is determinedin response to the fuel rail pressure decay rate of the fuel pressure inthe common fuel rail being greater than the decay threshold after thefirst designated duration, it may indicate that a fuel leak exists inthe higher-pressure region of the liquid fuel system between the IMV andthe fuel injectors. If the leak is indicated in response to the fuelpressure being less than the fuel rail pressure threshold for the seconddesignated duration where the engine fuel pressure is greater than theengine fuel pressure threshold and the engine speed in a designatedengine speed range, it may indicate that a gross fuel leak exists in theliquid fuel system or a component has degraded, since fuel pressurecannot build up in the common fuel rail even though fuel is being pumpedby the low-pressure fuel pump. In such cases, the engine may beimmediately shutdown rather than performing the method of FIG. 6.

FIG. 6 is a flow chart illustrating a method 600 for differentiatingbetween an external leak and an internal leak of a liquid fuel system,such as the liquid fuel system described above with respect to FIGS.2-3. An external leak may include a crack in a fuel supply line or thefuel rail, a faulty/leaky fuel injector, or other type of degradationwhere fuel leaks out of the system, for example to the engine or to theambient environment. In contrast, an internal leak may include adegraded check valve in a high-pressure fuel pump (e.g., check valve 350of FIG. 3) that causes fuel to leak out of the high-pressure region(downstream of the high-pressure pump) and into the low-pressure region(upstream of the high-pressure pump). While such a leak may reduceefficiency of the high-pressure pump, it does not pose risk of engine orvehicle degradation. Thus, method 600 differentiates between the twotypes of leaks in order to prevent an unnecessary emergency engineshutdown. Method 600 may be performed in response to an indication thata liquid fuel system leak is present, as described above. In otherexamples, method 600 may be performed during other times when fuelsystem pressure and/or flow rate measurements are available.

At 602, method 600 includes plotting leak flow rate as a function ofliquid fuel system pressure, which may be the same as the liquid fuelrail pressure or may be a pressure measurement elsewhere in the fuelsystem. The leak flow rate may be determined by output from a fuel flowsensor, based on fuel rail pressure, or other suitable mechanisms. Thedetermined leak flow rate and system pressure plotted in 602 may be datacollected during the leak test described above, or may be data collectedduring a subsequent test.

At 604, method 600 determines if the leak flow rate increases as liquidfuel rail pressure decreases. Many types of degradation that result inan external fuel system leak, such as a crack in a pipe comprising afuel supply line, for example, exhibit larger leak flow rates whensystem pressure is higher, and the leak flow rate may lessen as thepressure wanes. This is because the higher pressure in the supply lineor fuel rail forces more fuel out of the leak flow path; once less fuelis present in the supply line or rail, less pressure is exerted on theleak flow path and thus less fuel flows out of it. In contrast, adegraded check valve may remain seated in its valve seat during higherpressure conditions, due to the high pressure acting against the checkvalve. Once the system pressure decreases, the valve may begin to moveout of its valve seat, opening up the leak flow path. Thus, an internalleak caused by a faulty check valve may be identified based on thedirectionality of the leak flow rate as system pressure decreases,namely if the leak flow rate actually increases as the pressuredecreases.

FIG. 7 is a diagram 700 that depicts leak flow rate as a function ofsystem pressure for an internal leak (depicted by curve 702) and anexternal leak (depicted by curve 704). While the leak flow rate plottedon the vertical axis increases away from the intercept with thehorizontal axis, the system pressure plotted on the horizontal axisdecreases away from the intercept with the vertical axis. As shown indiagram 700, the internal leak exhibits increasing leak flow rate withdecreasing system pressure. In contrast, the external leak exhibitsdecreasing leak flow rate with decreasing system pressure.

Returning to FIG. 6, if it is determined at 604 that the leak flow rateincreases with decreasing system pressure, method 600 proceeds to 606 toindicate an internal leak, and, at 608, maintain current operatingparameters. In some examples, an operator of the vehicle may be notifiedof the internal leak and/or a diagnostic code may be set. Method 600then returns.

If it is determined at 604 that the leak flow rate does not increasewith decreasing system pressure, method 600 proceeds to 610 to indicatean external leak, and, at 612, shutdown the engine. In some examples, anoperator of the vehicle may be notified of the internal leak and/or adiagnostic code may be set. As one example of notifying a vehicleoperator, a fuel leak indicator light may be turned on in response tothe indication of the internal or the external leak.

Thus, the methods described above with respect to FIGS. 5-6 provide formonitoring a liquid fuel system to determine if a leak is present in thefuel system. In one example, the controller determines if a leak ispresent in the fluid system based on a first pressure decay rate of theliquid fuel system. If a leak is detected, the leak may be classified asan internal leak where the leaking fuel is not exposed to theenvironment or an external leak where the leaking fuel is exposed to theenvironment. In one example, responsive to identifying that a leak ispresent in the fluid system, the controller is configured todifferentiate between an internal leak and an external leak based on aleak flow rate as system pressure decreases. For example, the leak maybe classified as internal vs. external based on the directionality ofthe leak flow rate as system pressure decreases. If the leak isdetermined to be an internal leak, engine operation may continue due tothe lack of exposure of the fuel to the environment. In contrast, if anexternal leak is detected, the engine may be shutdown.

While the leak determination and classification described above isapplied to a fuel system including a high-pressure pump and fuel rail,similar concepts may be applied to other systems that include apressurized fluid downstream of a check valve, e.g., coolant deliverysystems.

FIG. 8 is a flow chart illustrating a method 800 for removing gaseousfuel in a gaseous fuel rail. Method 800 may be carried out according toinstructions stored in memory of a controller, such as controller 110,in combination with one or more sensors and/or actuators. For example,method 800 may be carried out by controller 110 in order to adjustgaseous fuel supply valve 334, one or more of the gas admission valves(e.g., valves 236, 322, 324, and/or 326), one or more of the liquid fuelinjectors (e.g., injectors 226, 308, 310, 312), ignition source 362,and/or vent valve 366. Method 800 may be carried out in response toreceiving a request to perform a non-emergency engine shutdown, asdescribed above with respect to FIG. 4.

At 802, method 800 includes closing a gaseous fuel supply valve. Oncethe request to shut down the engine is received, the gaseous fuel supplyvalve may be closed to block flow of additional gaseous fuel into thegaseous fuel rail. Once the flow of gaseous fuel is blocked fromreaching the gaseous fuel rail, any additional gaseous fuel trapped inthe gaseous fuel rail (e.g., between the gaseous fuel supply valve andplurality of gas admission valves) may be removed before the engine isshut down or before the engine is restarted. Any one or more of thebelow-described mechanisms may be executed in order to remove thegaseous fuel.

At 804, method 800 includes removing the trapped gaseous fuel byselectively fueling one or more cylinders of the engine with gaseousfuel. Selectively fueling the engine with gaseous fuel may include skipfiring the engine and supplying both liquid and gaseous fuel to a subsetof cylinders of the engine, as indicated at 806. During the skip fireoperation, only a subset of cylinders (e.g., one) receives fuel forcombustion, while the remaining cylinders do not undergo combustion. Asused herein, subset of cylinders includes at least one cylinder but lessthan all cylinders of the plurality of cylinders of the engine. Thegaseous fuel supplied to the active subset of cylinders may be combustedby injected liquid fuel. By operating only a subset of cylinders, theamount of fuel supplied to each active cylinder may be increasedrelative to when all cylinders are active, thus enabling operation withgaseous fuel. In contrast, during engine idle conditions prior toshutdown, if all cylinders are active, the amount of gaseous fuelavailable to supply to the cylinders may be too low to sustaincombustion of the gaseous fuel.

The number of cylinders selected to be in the subset of cylinders (e.g.,the number of cylinders selected to receive both liquid and gaseousfuel) may be based on the amount of gaseous fuel trapped in the gaseousfuel rail. For example, the gaseous fuel flow rate and/or gaseous fuelrail pressure may be determined when the shutdown request is receivedand the number of cylinders selected to receive gaseous and liquid fueldetermined based on the flow rate or pressure, such that as the flowrate or pressure of the gaseous fuel increases, the number of selectedcylinders increases. The number of selected cylinders may further bebased on one or more of an upper limit gaseous fuel substitution ratioor a lower limit gaseous fuel substitution ratio, when the engine isconfigured to combust the gaseous fuel with liquid fuel injection. Thesubstitution ratio refers to the amount of power derived from gaseousfuel to liquid fuel, and is selected and/or limited by engine operatingconditions such as engine speed. Thus the upper limit gaseous fuelsubstitution ratio may indicate the maximum amount of gaseous fuel thatcan be provided to a cylinder and the lower limit gaseous fuelsubstitution ratio may indicate the minimum amount of gaseous fuelneeded to sustain combustion of the gaseous fuel.

In another example, selectively fueling the engine with gaseous fuel mayinclude skip firing the engine and supplying only gaseous fuel to asubset of cylinders and only liquid fuel to remaining cylinders of theengine, as indicated at 808. In this way, combustion may occur only inthe cylinders receiving liquid fuel and not in the cylinders receivinggaseous fuel. The gaseous fuel trapped in the gaseous fuel rail is thuspassed through the engine.

In a further example, selectively fueling the engine with gaseous fuelincludes supplying gaseous fuel the engine when the engine is turningbut not combusting, as indicated at 810. This may include when theengine is being cranked by the starter motor during an engine start,when the engine is spinning down during the engine shut down, when theengine is being turned by an alternator, or other condition wherecombustion is not needed but the engine still turns. To preventcombustion from occurring, no liquid fuel or other ignition source isprovided to the cylinders, and thus the gaseous fuel in the gaseous fuelrail and/or gaseous fuel in the cylinders is directed out of the engine.

Removing the trapped gaseous fuel may be performed without routing thegaseous fuel through the engine. To remove the gaseous fuel in thismanner, method 800 may include, at 812, opening the vent valve in thevent line coupled to the gaseous fuel rail and activating the ignitionsource in the vent line to combust the gaseous fuel. By opening the ventvalve, the gaseous fuel in the gaseous fuel rail may be directed out ofthe rail and through the vent line. Before reaching atmosphere, thegaseous fuel may be combusted via the ignition source. To confirm thatthe gaseous fuel is being combusted and not released to atmosphere, atemperature sensor may be positioned near the ignition source. If thegaseous fuel is not combusted by the ignition source, the vent valve maybe closed and the gaseous fuel may be removed by another mechanism.

At 814, method 800 includes shutting down the engine, for example bystopping liquid fuel injection. The shutting down of the engine may beperformed after the gaseous fuel is removed from the gaseous fuel rail,as indicated at 816. This may include shutting down the engine inresponse to an indication that the gaseous fuel is removed from thegaseous fuel rail, for example in response to feedback from a gaseousfuel rail pressure sensor or after a threshold amount of time haselapsed. In one example where the gaseous fuel is removed via skipfiring the engine with both liquid and gaseous fuel provided to a subsetof the cylinders (and not the remaining cylinders), as described aboveat 806, the engine may be shut down after a predetermined number ofengine cycles has occurred, where the number of engine cycles is basedon the amount of gaseous fuel originally in the rail, number of selectedactive cylinders, and the amount of gaseous fuel supplied to eachcylinder.

A further example mechanism for removing trapped gaseous fuel may beperformed after engine shutdown. As indicated at 818, the gaseous fuelthat remains in the gaseous fuel rail may be expanded in an expansionchamber, such as chamber 360 of FIG. 3, that is fluidically coupled tothe gaseous fuel rail. The additional volume provided by the expansionchamber may allow the gaseous fuel to reach atmospheric pressure,whereby it will no longer expand across the gas admission valves andinto the engine. The gaseous fuel in the expansion chamber may bedirected back to the gaseous fuel rail prior to or during a subsequentengine operation, as indicated at 820, via introduction of intakemanifold pressure or via activation of an actuator of the chamber.Method 800 then returns.

Thus, method 800 described above provides for removing gaseous fuelbetween a gaseous fuel supply valve and the gas admission valves of thegaseous fuel system. The gaseous fuel may be removed prior to shuttingdown the engine or it may be removed after engine shutdown but before asubsequent engine start. The gaseous fuel may be supplied to the engine,where it may either be combusted or travel through the engineuncombusted. Additionally or alternatively, the gaseous fuel may bevented out of the gaseous fuel rail via a vent line. The gaseous fuel inthe vent line may be combusted and then released to atmosphere, or itmay be stored in an expansion chamber and then directed back to the railduring an engine start. By doing so, the gaseous fuel may be preventedfrom expanding into the engine, where it could disrupt combustion duringa subsequent engine start.

An example of a system includes a fluid system configured to maintain afluid at a pressure downstream of a check valve; and a controllerconfigured to: determine if a leak is present in the fluid system basedon a first pressure decay rate of the fluid system; and responsive toidentifying that a leak is present in the fluid system, differentiatebetween an internal leak and an external leak based on a leak flow rateas fluid system pressure decreases.

In a first example of the above system, the controller is configured todifferentiate between an internal leak and an external leak based on adirectionality of a change in the leak flow rate as the fluid systempressure decreases. A second example of the system may optionallyinclude the first example and additionally or alternatively includeswherein the fluid system comprises a fuel system of an engine includinga high-pressure pump to deliver fuel to a fuel rail, and wherein thecheck valve is positioned in the high-pressure fuel pump. A thirdexample of the system optionally includes one or more of the first andsecond examples, and additionally or alternatively includes wherein thecontroller is configured to determine the leak is an internal leak ifthe leak flow rate increases as pressure in the fuel system decreases. Afourth example of the system optionally includes one or more of thefirst, second, and third examples, and additionally or alternativelyincludes wherein the controller is configured to determine the leak isan external leak if the leak flow rate decreases as pressure in the fuelsystem decreases. A fifth example of the system optionally includes oneor more of the first, second, third, and fourth examples, andadditionally or alternatively includes wherein the controller isconfigured to maintain engine operation in response to determining thatthe leak is an internal leak and shut down the engine in response todetermining that the leak is an external leak. A sixth example of thesystem optionally includes one or more of the first, second, third,fourth, and fifth examples, and additionally or alternatively includeswherein the leak flow rate is estimated based on a second pressure decayrate.

Another example of a system includes a gaseous fuel supply system tosupply gaseous fuel from a gaseous fuel storage source to an enginehaving a plurality of cylinders; and a controller configured to detect arequest to shut down the engine; and in response to detecting therequest, remove gaseous fuel trapped within the gaseous fuel supplysystem by closing a gaseous fuel supply valve and selectively fuelinggaseous fuel to the engine.

In a first example of the above system, the gaseous fuel supply systemcomprises a gaseous fuel rail including a plurality of gas admissionvalves, each gas admission valve to supply gaseous fuel to a respectivecylinder of the plurality of cylinders, wherein the gaseous fuel supplyvalve is located upstream of the gaseous fuel rail, and wherein thegaseous fuel trapped within the gaseous fuel supply system is trappedbetween the gaseous fuel supply valve and plurality of gas admissionvalves. A second example of the above system optionally includes thefirst example and additionally or alternatively includes wherein theengine is configured to combust liquid fuel and gaseous fuel, wherein toselectively fuel gaseous fuel to the engine, the controller isconfigured to supply both gaseous fuel and liquid fuel to each cylinderof a subset of cylinders of the plurality of cylinders, thereby tocombust the gaseous fuel trapped within the gaseous fuel supply system,the subset including at least one cylinder but less than all cylindersof the plurality of cylinders. A third example of the system optionallyincludes one or more of the first and second examples and additionallyor alternatively includes wherein a number of cylinders in the subset ofcylinders is selected based on one or more of an initial gaseous fuelsupply system pressure, an upper limit gaseous fuel substitution ratio,a lower limit gaseous fuel substitution ratio, or a threshold timelimit. A fourth example of the system optionally includes one or more ofthe first, second, and third examples and additionally or alternativelyincludes wherein in response to detecting that the gaseous fuel trappedwithin the gaseous fuel supply system has been removed, the controlleris further configured to shut down the engine. A fifth example of thesystem optionally includes one or more of the first, second, third, andfourth examples and additionally or alternatively includes wherein theengine is configured to combust liquid fuel and gaseous fuel, wherein toselectively fuel gaseous fuel to the engine, the controller isconfigured to supply only gaseous fuel to a subset of cylinders of theplurality of cylinders and to combust only liquid fuel in remainingcylinders of the plurality of cylinders. A sixth example of the systemoptionally includes one or more of the first, second, third, fourth, andfifth examples and additionally or alternatively includes wherein toselectively fuel gaseous fuel to the engine, the controller isconfigured to supply only gaseous fuel to the engine while the engine isturning but combustion is not occurring prior to an engine restartfollowing the request to shut down the engine. A seventh example of thesystem optionally includes one or more of the first, second, third,fourth, fifth, and sixth examples and additionally or alternativelyincludes an expansion chamber fluidically coupled to the gaseous fuelsupply system. An eighth example of the system optionally includes oneor more of the first, second, third, fourth, fifth, sixth, and seventhexamples and additionally or alternatively includes an ignition sourcefluidically coupled to the gaseous fuel supply system via a vent lineand a vent valve positioned in the vent line between the gaseous fuelsupply system and the ignition source, and wherein the controller isconfigured to further remove gaseous fuel trapped within the gaseousfuel supply system by opening the vent valve and activating the ignitionsource in response to the request to shut down the engine.

A further example of a system includes an engine having a plurality ofcylinders configured to combust liquid fuel and gaseous fuel; a gaseousfuel supply system including a gaseous fuel rail having a plurality ofgas admission valves, each gas admission valve to supply gaseous fuel toa respective cylinder of the plurality of cylinders, and a gaseous fuelsupply valve located upstream of the gaseous fuel rail; an expansionchamber fluidically coupled to the gaseous fuel supply system; and acontroller configured to detect a request to shut down the engine; andin response to detecting the request, remove gaseous fuel trapped withinthe gaseous fuel supply system by closing the gaseous fuel supply valveand expanding the gaseous fuel in the expansion chamber.

In a first example of the above system, the controller is furtherconfigured to, in response to a subsequent request to restart the enginefollowing the shutdown of the engine, direct the gaseous fuel in theexpansion chamber back to the gaseous fuel supply system. A secondexample of the system optionally includes the first example andadditionally or alternatively includes an ignition source fluidicallycoupled to the gaseous fuel supply system via a vent line and a ventvalve positioned in the vent line between the gaseous fuel supply systemand the ignition source, and wherein the controller is configured tofurther remove gaseous fuel trapped within the gaseous fuel supplysystem by opening the vent valve and activating the ignition source inresponse to the request to shut down the engine. A third example of thesystem optionally includes one or more of the first or second examplesand additionally or alternatively includes wherein the controller isconfigured to further remove gaseous fuel trapped within the gaseousfuel supply system by selectively fueling gaseous fuel to the engineafter closing the gaseous fuel supply valve.

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralof said elements or steps, unless such exclusion is explicitly stated.Furthermore, references to “one embodiment” of the present invention arenot intended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features. Moreover, unlessexplicitly stated to the contrary, embodiments “comprising,”“including,” or “having” an element or a plurality of elements having aparticular property may include additional such elements not having thatproperty. The terms “including” and “in which” are used as theplain-language equivalents of the respective terms “comprising” and“wherein.” Moreover, the terms “first,” “second,” and “third,” etc. areused merely as labels, and are not intended to impose numericalrequirements or a particular positional order on their objects.

This written description uses examples to disclose the invention,including the best mode, and also to enable a person of ordinary skillin the relevant art to practice the invention, including making andusing any devices or systems and performing any incorporated methods.The patentable scope of the invention is defined by the claims, and mayinclude other examples that occur to those of ordinary skill in the art.Such other examples are intended to be within the scope of the claims ifthey have structural elements that do not differ from the literallanguage of the claims, or if they include equivalent structuralelements with insubstantial differences from the literal language of theclaims.

1. A system, comprising: a gaseous fuel supply system to supply gaseousfuel from a gaseous fuel storage source to an engine having a pluralityof cylinders; and a controller configured to: detect a request to shutdown the engine; and in response to detecting the request, removegaseous fuel trapped within the gaseous fuel supply system by closing agaseous fuel supply valve and selectively fueling gaseous fuel to theengine.
 2. The system of claim 1, wherein the gaseous fuel supply systemcomprises a gaseous fuel rail including a plurality of gas admissionvalves, each gas admission valve to supply gaseous fuel to a respectivecylinder of the plurality of cylinders, wherein the gaseous fuel supplyvalve is located upstream of the gaseous fuel rail, and wherein thegaseous fuel trapped within the gaseous fuel supply system is trappedbetween the gaseous fuel supply valve and plurality of gas admissionvalves.
 3. The system of claim 1, wherein the engine is configured tocombust liquid fuel and gaseous fuel, wherein to selectively fuelgaseous fuel to the engine, the controller is configured to supply bothgaseous fuel and liquid fuel to each cylinder of a subset of cylindersof the plurality of cylinders, thereby to combust the gaseous fueltrapped within the gaseous fuel supply system, the subset including atleast one cylinder but less than all cylinders of the plurality ofcylinders.
 4. The system of claim 3, wherein a number of cylinders inthe subset of cylinders is selected based on one or more of an initialgaseous fuel supply system pressure, an upper limit gaseous fuelsubstitution ratio, a lower limit gaseous fuel substitution ratio, or athreshold time limit.
 5. The system of claim 3, wherein in response todetecting that the gaseous fuel trapped within the gaseous fuel supplysystem has been removed, the controller is further configured to shutdown the engine.
 6. The system of claim 1, wherein the engine isconfigured to combust liquid fuel and gaseous fuel, wherein toselectively fuel gaseous fuel to the engine, the controller isconfigured to supply only gaseous fuel to a subset of cylinders of theplurality of cylinders and to combust only liquid fuel in remainingcylinders of the plurality of cylinders.
 7. The system of claim 1,wherein to selectively fuel gaseous fuel to the engine, the controlleris configured to supply only gaseous fuel to the engine while the engineis turning but combustion is not occurring prior to an engine restartfollowing the request to shut down the engine.
 8. The system of claim 1,further comprising a gaseous fuel canister fluidically coupled to thegaseous fuel supply system, where the controller is configured to open avent valve in a vent line coupled between the gaseous fuel canister andthe gaseous fuel rail in response to receiving the request to shut downthe engine.
 9. The system of claim 1, further comprising an ignitionsource fluidically coupled to the gaseous fuel supply system via a ventline and a vent valve positioned in the vent line between the gaseousfuel supply system and the ignition source, and wherein the controlleris configured to further remove gaseous fuel trapped within the gaseousfuel supply system by opening the vent valve and activating the ignitionsource in response to the request to shut down the engine.
 10. A system,comprising: an engine having a plurality of cylinders configured tocombust liquid fuel and gaseous fuel; a gaseous fuel supply systemincluding a gaseous fuel rail having a plurality of gas admissionvalves, each gas admission valve to supply gaseous fuel to a respectivecylinder of the plurality of cylinders, and a gaseous fuel supply valvelocated upstream of the gaseous fuel rail; an expansion chamberfluidically coupled to the gaseous fuel supply system; and a controllerconfigured to: detect a request to shut down the engine; and in responseto detecting the request, remove gaseous fuel trapped within the gaseousfuel supply system by closing the gaseous fuel supply valve andexpanding the gaseous fuel in the expansion chamber.
 11. The system ofclaim 10, wherein the controller is further configured to, in responseto a subsequent request to restart the engine following the shutdown ofthe engine, direct the gaseous fuel in the expansion chamber back to thegaseous fuel supply system.
 12. The system of claim 10, furthercomprising an ignition source fluidically coupled to the gaseous fuelsupply system via a vent line and a vent valve positioned in the ventline between the gaseous fuel supply system and the ignition source, andwherein the controller is configured to further remove gaseous fueltrapped within the gaseous fuel supply system by opening the vent valveand activating the ignition source in response to the request to shutdown the engine.
 13. The system of claim 10, wherein the controller isconfigured to further remove gaseous fuel trapped within the gaseousfuel supply system by selectively fueling gaseous fuel to the engineafter closing the gaseous fuel supply valve.
 14. A system, comprising: afluid system in an engine configured to maintain a fluid at a pressuredownstream of a check valve; and a controller configured to: determineif a leak is present in the fluid system based on a first pressure decayrate of the fluid system; responsive to identifying that a leak ispresent in the fluid system, differentiate between an internal leak andan external leak based on a leak flow rate as fluid system pressuredecreases; and maintain engine operation in response to determining thatthe leak is an internal leak and shut down the engine in response todetermining that the leak is an external leak.
 15. The system of claim14, wherein the fluid system comprises a fuel system of an engineincluding a high-pressure pump to deliver fuel to a fuel rail, andwherein the check valve is positioned in the high-pressure fuel pump.16. The system of claim 15, wherein the controller is configured todetermine the leak is an internal leak if the leak flow rate increasesas pressure in the fuel system decreases.
 17. The system of claim 15,wherein the controller is configured to determine the leak is anexternal leak if the leak flow rate decreases as pressure in the fuelsystem decreases.
 18. The system of claim 14, wherein the leak flow rateis estimated based on a second pressure decay rate.
 19. The system ofclaim 14, further comprising an indicator light configured to beilluminated based on the determination of an external leak or aninternal leak.